1. Field of the Invention
The present invention relates to an electrical switching apparatus operating mechanism and, more specifically to a catchment mechanism structured to prevent over rotation of a closing assembly cam.
2. Background Information
Electrical switching apparatus, typically, include a housing, at least one bus assembly having a pair of contacts, a trip device, and an operating mechanism. The housing assembly is structured to insulate and enclose the other components. The at least one pair of contacts include a fixed contact and a movable contact and typically include multiple pairs of fixed and movable contacts. Each contact is coupled to, and in electrical communication with, a conductive bus that is further coupled to, and in electrical communication with, a line or a load. A trip device is structured to detect an over current condition and to actuate the operating mechanism. An operating mechanism is structured to both open the contacts, either manually or following actuation by the trip device, and close the contacts.
That is, the operating mechanism includes both a closing assembly and an opening assembly, which may have common elements, that are structured to move the movable contact between a first, open position, wherein the contacts are separated, and a second, closed position, wherein the contacts are coupled and in electrical communication. The operating mechanism includes a rotatable pole shaft that is coupled to the movable contact and structured to move each movable contact between the closed position and the open position. Elements of both the closing assembly and the opening assembly are coupled to the pole shaft so as to effect the closing and opening of the contacts.
In the prior art, low and medium voltage electrical switching apparatus operating mechanisms typically had a stored energy device, such as an closing spring, and at least one link coupled to the pole shaft. The at least one link, typically, included two links that acted cooperatively as a toggle assembly. When the contacts were open, the toggle assembly was in a first, collapsed configuration and, conversely, when the contacts were closed, the toggle assembly was, typically, in a second, toggle position, that is, an in-line configuration, or in a slightly over-toggle position. An opening spring biased the pole shaft, and therefore the toggle assembly, to the collapsed position. The spring and toggle assembly were maintained in the second, toggle position by the trip device.
The trip device included an over-current sensor, a latch assembly and may have included one or more additional links that were coupled to the toggle assembly. Alternately, the latch assembly was directly coupled to the toggle assembly. When an over-current situation occurred, the latch assembly was released allowing the opening spring to cause the toggle assembly to collapse. When the toggle assembly collapsed, the toggle assembly link coupled to the pole shaft caused the pole shaft to rotate and thereby move the movable contacts into the open position.
In a low and medium voltage electrical switching apparatus, the force required to close the contacts was, and is, typically greater than what a human may quickly apply and, as such, the operating mechanism typically included a mechanical closing assembly to close the contacts. The closing assembly, typically, included at least one stored energy device, such as a spring, and/or a motor. Closing springs, typically, were about 2 inches in diameter and about 5 to 6 inches in length. These springs were structured to apply a force of about 1000 pounds. A common configuration included a motor that compressed one or more springs in the closing assembly. That is, the closing springs were coupled to a cam roller that engaged a cam coupled to the motor. As the motor rotated the cam, the closing springs were compressed or charged. The toggle assembly also included a cam roller, typically at the toggle joint. The closing assembly further included one or more cams disposed on a common cam shaft with the closing spring cam. Alternatively, depending upon the configuration of the cam, both the closing spring cam roller and the toggle assembly cam roller could engage the same cam. When the closing springs were released, the closing spring cam roller applied force to the associated cam and caused the cam shaft to rotate. That is, the cam roller “operatively engaged” the cam. Rotation of the cam shaft would also cause the cam associated with the toggle assembly cam roller to rotate. As the cam associated with the toggle assembly cam roller rotated, the cam caused the toggle assembly cam roller, and therefore the toggle assembly, to be moved into selected positions and/or configurations. More specifically, the toggle assembly was moved so as to rotate the pole shaft into a position wherein the contacts were closed. Thus, the stored energy from the closing springs was transferred via the cams, cam shaft, toggle assembly, and pole shaft to the contacts.
For example, during a closing procedure the toggle assembly would initially be collapsed and, therefore, the contacts were open. When the closing springs were released, the rotation of the cam associated with the toggle assembly cam roller would cause the toggle assembly to move back into the second, toggle position, thereby closing the contacts. This motion would also charge the opening springs. Prior to closing, the trip device latch would be reset thereby holding the toggle assembly in the second, toggle position. After the contacts were closed, it was common to recharge the closing spring so that, following an over current trip, the contacts could be rapidly closed again. That is, if the closing springs were charged, the contacts could be closed almost immediately without having to wait to charge the closing springs
While this configuration is effective, there are a substantial number of components required, each of which requires space to operate within and each of which are subject to wear and tear. Further, certain components are exposed to considerable force, which enhances wear and tear, during operations wherein that particular component is not in use. For example, in this configuration the cam used to charge the closing spring is still engaged with other components during the release of the closing spring. It is this operative engagement that causes enhanced wear and tear.